Hypothyroidism: Causes and Management

Hypothyroidism, also known as an underactive thyroid, is a condition in which the body’s thyroid gland does not produce enough thyroid hormones. The thyroid gland is at the front of the throat and produces two thyroid hormones: tri-iodothyronine (T3) and thyroxine (T4)…These hormones influence the speed of the body’s metabolism. This affects processes such as digestion, temperature and mood regulation. When the active thyroid hormones are reduced, slowing the body’s metabolism, causing a number of symptoms.

“I was diagnosed at age 38… I had been sleeping more and more…and my weight was slowly rising. I started treatment, and the relatively rapid change to feeling ‘normal’ again was stunning!” – Kirsteen, 48


There are several possible causes of hypothyroidism and the most common cause is the immune system attacking the thyroid gland. This damages the gland, meaning it releases less T3 and T4. One example of a condition in which the immune system attacks the thyroid is Hashimoto’s Thyroiditis.

In most cases there are no clear reasons why the immune system attacks the thyroid gland. Genes may play a role, as conditions such as Hashimoto’s Thyroiditis are more likely to occur if there are other people in the family with a history of thyroid problems, but also the environment in which these genes are exposed to may increase the risk of thyroid problems developing.

Another cause of hypothyroidism is the treatment for hyperthyroidism (overactive thyroid). In hyperthyroidism, the thyroid produces too much T3 and T4. Treatments, such as surgery or medications, aim to reduce T3 and T4 production. However, if thyroid hormone production is reduced too much, hypothyroidism then occurs, which requires treatment.

Other possible causes of hypothyroidism, (underactive thyroid), include:

  • Not enough iodine in the diet. This is because iodine is important for the formation of T3 and T4. This is more common is certain developing countries where there is a lack of iodine within soils, usually in mountainous areas.
  • Certain medications, such as lithium and rifampicin may affect thyroid function.
  • Disorders of other glands which influence the thyroid, such as the pituitary gland.
  • In babies, poor development of the thyroid gland in the womb can lead to an underactive thyroid. This rare condition is called ‘congenital hypothyroidism’. All babies in the UK are screened for this when they are born.

Treatment & Management

Most hypothyroidism is treated with a drug called levothyroxine, which is synthetic (man-made) T4.  Levothyroxine replaces the T4 the thyroid is not producing. This is then converted by the body to T3 which is the active form of the thyroid hormone.

To achieve optimal absorption, levothyroxine should be taken on an empty stomach, 30 minutes before taking other medications or food, at around the same time every day. Some people can feel better within a week or two, whereas for others it can take months for all symptoms to go away.

When starting treatment, regular blood tests measuring hormone levels help to determine the correct dose, as the dose required is different for each individual. Once the hormone levels are optimal and constant, blood tests are usually required once a year to check that these levels remain stable.

Levothyroxine is not commonly associated with significant side effects, as it is replacing a hormone that the body requires. Most side effects are due to the dose being incorrect. For example, if the dose is too high, symptoms of an overactive thyroid may occur (hyperthyroidism). If unexplained symptoms are experienced, someone being treated for hypothyroidism should seek a doctor.

Patients with hypothyroidism usually need to take levothyroxine for the rest of their lives to maintain normal hormone levels. In the UK, these patients are eligible for a medical exemption certificate, which means they do not have to pay for their prescriptions of levothyroxine, and all other NHS provided medications.

Besides having to take a daily tablet, most people with hypothyroidism can usually lead normal lives.

Read more about Kirsteen’s story with The Doctor Service

The Doctor Service provides further health information and a variety of treatments on their website.

Resources for patients

Edited by Dr Kiran Sodha & The Doctor Service


  1. Bray, J., Cragg, P. and Macknight, A. (1994). Lecture notes on human physiology. 3rd ed. Oxford: Blackwell Science.
  2. Nhs.uk. (2017). NHS Choices Home Page. [online] Available at: http://www.nhs.uk [Accessed 20 Jun. 2017].
  3. Rubenstein, D., Wayne, D. and Bradley, J. (1997). Lecture notes on clinical medicine. 5th ed. Malden, MA: Blackwell Science.
  4. Vaidya, B. and Pearce, S. (2008). Management of hypothyroidism in adults. BMJ, 337(jul28 1), pp.a801-a801.
Leave a Reply

Your email address will not be published. Required fields are marked *